**2.1 Inoculum, medium and procedures**

Photoheterotrophic bacteria *Rhodobacter sphaeroides* O.U. 001 ATTC 4919 (Fig.1) were cultivated on Van Niel's medium containing: K2HPO4 (1.0 g/l), MgSO4 (0.5 g/l), yeast extract (10g/l) and tap water filled up to 1 l and then activated according to the procedure already described (Waligórska, 2006). For hydrogen generation a modified Biebl and Pfennig medium (Biebl, 1981) was applied. This standard medium contained: KH2PO4 (0.5 g/l); MgSO4\*7H2O (0.2 g/l); NaCl (0.4 g/l); CaCl2\*2H2O (0.05 g/l), L-malic (2.0 g/l); sodium glutamate (0.36 g/l), ferric tartrate (0.005 g/l); yeast extract (0.17 g/l) and microelements: ZnCl2 (0.07 g/l); MnCl2\*4H2O (0.1 g/l); H3BO3 (0.06 g/l); CoCl2\*6H2O (0.2 g/l); CuCl2\*2H2O (0.02 g/l); NiCl2\*6H2O (0.02 g/l); Na2MoO4\*2H2O (0.04 g/l); HCl 25% (1ml/1).

The untreated food waste were initially filtered through cotton wool, next sterilized at 120oC by autoclaving for 20 min and re-filtered applying paper filter.

Wastes with different COD values (46 g O2/l for dairy wastes, 220 and 27 g O2/l for brewery wastes) after pretreatment were introduced to the medium, which did not contain L-malic acid. The medium was inoculated with bacteria 30% v/v (0.36 g dry wt/l). The process was performed in small vials (25 ml) made from sodium glass and filled with 12.5 ml of inoculated medium. Tightly closed vials were carefully deaerated with argon before starting the illumination. All experiments were carried out at 28 ± 2oC and pH after sterilization and inoculation varied between 7.0 and 7.2. The mercury-tungsten lamp (Ultra-Vitalux –300W from Osram) was applied in all experiments. The intensity of light during hydrogen generation was 9 klx (116 W/m2). The vials with Biebl and Pfenniga standard medium was used as reference (Biebl, 1981).
